Michael Thielen
Extrusion Blow Molding,
Table of contents
Preface ...... V
The Author ...... VI
1 Introduction ...... 1 1.1 Hollow Plastic Parts – What Are They for?...... 1 1.2 Processes to Produce Hollow Plastic Parts ...... 1 1.2.1 Thermoplastics ...... 1 1.2.2 Thermosets ...... 2 1.3 Application Areas for Blow Molded Hollow Parts ...... 3 1.4 History of Blow Molding Hollow Parts ...... 8
2 Extrusion Blow Molding ...... 15 2.1 Process Sequence for Extrusion Blow Molding ...... 15 2.2 Raw Materials ...... 17 2.2.1 Plastics ...... 17 2.2.2 Plastics for Extrusion Blow Molding ...... 22 2.3 Machine Technology ...... 24 2.3.1 Basic Structure of a Blow Molding Machine ...... 24 2.3.2 Extruders and Screws ...... 24 2.3.2.1 Smooth-Bore Extruder ...... 25 2.3.2.2 Extruder with Grooved Feed Zone ...... 27 2.3.2.3 Gravimetric Throughput Control ...... 30 2.3.3 Parison Heads ...... 32 2.3.3.1 Spider Heads ...... 32 Contents
2.3.3.2 Mandrel Heads ...... 34 2.3.3.3 Spiral Heads ...... 36 2.3.4 Continuous/Discontinuous Extrusion ...... 38 2.3.5 Wall Thickness Control ...... 41 2.3.5.1 Swelling Behavior of the Parison ...... 43 2.3.6 Systems for Influencing the Radial Wall Thickness Distribution ...... 46 2.3.6.1 Why Radial Wall Thickness Control? ...... 46 2.3.6.2 Statically Flexible Deformable Ring (SFDR®) ...... 46 2.3.6.3 Partial Wall Thickness Distribution System (PWDS®) . 47 2.3.6.4 Wall Thickness Layer Control ...... 52 2.3.7 Clamping Units ...... 56 2.3.8 Controls ...... 61 2.3.8.1 IPC Control (Industrial PC) ...... 63 2.3.9 Cooling ...... 64 2.3.9.1 Shrinkage and Warpage ...... 64 2.3.10 Air ...... 67 2.3.11 Single-/Multiple-Head Systems ...... 68 2.3.11.1 Long Stroke Machines ...... 69 2.3.12 Single/Double Station Machines ...... 70 2.3.12.1 Combinations of the Two Principles ...... 71 2.3.13 Rotary-Wheel Blow Molding Systems ...... 72 2.4 Blow Molding Tools ...... 74 2.4.1 Mold Layout ...... 74
2.4.1.1 Prototype Molds in Cast Resin Construction ...... 75 2.4.1.2 Prototype Molds with Metal Surface and Cast Resin Backing ...... 75 2.4.1.3 Cast Metal Prototype Molds ...... 75 2.4.1.4 Aluminum Prototype Molds ...... 76 2.4.1.5 Mass-Production Molds ...... 76 2.4.2 Design Guidelines ...... 79 2.4.2.1 Blow Mold Guide ...... 79 2.4.2.2 Cutting Edges ...... 79
Contents
2.4.2.3 Mold Support ...... 82 2.4.2.4 Mold Venting ...... 82 2.4.3 Blow Mold Cooling ...... 84 2.4.3.1 Drilled Cooling ...... 84 2.4.3.2 Milled Cooling ...... 85 2.4.3.3 Cast-in Pipe Cooling ...... 85 2.4.4 Blow Mold Accessories ...... 87 2.4.4.1 Masks ...... 87 2.4.4.2 Spreader Pins ...... 87 2.4.4.3 Blow Pin ...... 88 2.4.4.4 Calibration Pin and Calibration Blow Pin ...... 89 2.4.4.5 Blow Needle ...... 90 2.4.4.6 Parison Closing Device ...... 92 2.4.4.7 Stripper Plate ...... 92 2.4.4.8 Head Tool (Die and Core) ...... 92 2.4.4.9 Set-up Socket ...... 93 2.4.5 Process-Integrated Follow-up Procedures ...... 93 2.4.5.1 Post-Cooling with a Post-Cooling Mold ...... 93 2.4.5.2 Complete Processing in the Blow Molding Machine . . 94 2.4.6 Injection Blow Molding and Dip Blow Molding ...... 96 2.4.7 Use of Computers in Blow Mold Construction ...... 97 2.5 Downstream and Auxiliary Equipment ...... 98 2.5.1 Cooling Units ...... 99 2.5.2 Compressors ...... 100 2.5.3 Dryer ...... 100 2.5.4 Deflashing ...... 100 2.5.5 Grinder ...... 101 2.5.6 Material Handling ...... 102 2.5.7 Post-Cooling ...... 104 2.5.8 Leak Test ...... 105 2.5.9 Filling ...... 106 2.5.10 Capping/Closing ...... 106 2.5.11 Labeling ...... 106 Contents
2.5.12 Printing ...... 106 2.5.13 Packaging ...... 106 2.5.14 Further Peripheral Devices ...... 107 2.6 Special Process Variants ...... 107 2.6.1 Multilayer/Coextrusion Blow Molding ...... 107 2.6.1.1 Coextrusion with Barrier Layer ...... 108 2.6.1.2 Machine Technology for Multilayer/Coextrusion ...... 108 2.6.1.3 Plastic Fuel Tank (PFT) ...... 109 2.6.2 Sheet Forming for the Production of Fuel Tanks ...... 114 2.6.3 3D Blow Molding ...... 114 2.6.3.1 Different Machine Technologies ...... 117 2.6.3.2 3D Blow Molding and Coextrusion with Barrier Layer ...... 122 2.6.3.3 Radial Wall Thickness Control ...... 122 2.6.4 Sequential Coextrusion ...... 123 2.6.4.1 Process Technology of Sequential Coextrusion ...... 125 2.6.4.2 Machine Technology of Sequential Coextrusion ...... 126 2.6.4.3 Production Target: Stable Processing Conditions ...... 127 2.6.5 Extrusion Blow Molding of Polycarbonate Water Bottles ...... 128 2.6.5.1 Advantages of PC ...... 129 2.6.5.2 Machine Technology for PC Water Bottles ...... 130 2.6.6 In-Mold Labeling ...... 131 2.6.7 View Stripe Equipment ...... 132 2.6.8 In-Mold Decoration ...... 133 2.6.9 Blow Molding Foam Technology (BFT) ...... 134 2.6.10 MuCell ...... 136 2.6.11 Blow Molding of Fiber-Reinforced Thermoplastics ...... 138 2.6.12 Blow-Fill-Seal Process ...... 138
3 Product Development ...... 143 3.1 Product Trials and Testing ...... 144 3.2 Designing for Blow Molding ...... 145 3.3 CAE, Simulation Procedures: Process and Product Simulation ...... 149
Contents
3.4 Product Development in Extrusion Blow Molding ...... 151 3.5 Feasibility Analysis Sandbox ...... 152 3.6 Calculation of the Internal Burst Pressure of a Windshield Wiper Water Tank ...... 154
4 The Blow Molding Operation ...... 159 4.1 From the Idea to the Product ...... 159 4.2 Changeover ...... 165 4.3 Layout of a Blow Molding Process ...... 168
5 Recycling in Extrusion Blow Molding Technology ...... 171 5.1 Possible Strategies for Processing Regrind ...... 172 5.2 Layer Structures for Blow Molded Parts with Recycled Material ...... 173 5.3 Recycling in Six-Layer Coextrusion...... 174 5.4 Preparation of the Material ...... 176 5.5 Material Conveying, Dosing, and Plastification ...... 176 5.6 Mass Flow Rate ...... 178 5.7 Avoiding Defects ...... 180 5.8 Blow Head, Blow Mold, and Blow Molding Process ...... 180
Appendix: Formula Symbols, Abbreviations, and Short Codes ...... 183
Index ...... 187